Farnesoid X receptor (FXRα, NR1H4) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors and was cloned in 1995 (Forman B. M. et al., Cell, 1995, 81, 687-693; Seol W. et al., Mal. Endocrinol., 1995, 9, 72-85).
FXR is highly expressed in the liver, intestine, kidney, adrenal glands, white adipose tissue and is induced during adipocyte differentiation in vitro (Cariou B. et al., J. Biol. Chem., 2006, 16, 11039-11049).
FXR contains a conserved DNA-binding domain (DBD) and a C-terminal ligand binding domain (LBD). The farnesoid X receptor-RXR heterodimer binds with highest affinity to an inverted repeat-1 (IR-1) response element, in which consensus receptor-binding hexamers are separated by one nucleotide. The farnesoid X receptor is part of an interrelated process, in that the receptor is activated by bile acids (the end product of cholesterol metabolism) (see, e.g., Makishima M. et al., Science, 1999, 284, 1362-1365; Parks D. J. et al., Science, 1999, 284, 1365-1368; Wang H. et al., Mol. Cell., 1999, 3, 543-553), which serve to inhibit cholesterol catabolism. See also, Urizar N. L. et al., J. Biol. Chem., 2000, 275, 39313-39317. The single FXRα gene in humans and mice encodes 4 FXRs isoforms (FXRα1, FXRα2, FXRα3 and FXRα4). They differ by their N-terminus and by the insertion/deletion of four amino acids in the hinge region. Many target genes are regulated in an isoform-independent manner.
The second FXR gene FXRβ (NR1H5) has been identified in rodents, dogs and chicken but is a pseudogene in primates and in human (Otte K. et al., Mol. Cell. Biol., 2003, 23, 864-872). FXRβ is a lanosterol sensor and its physiological function remains unclear.
FXR regulates diverse physiological processes. This nuclear receptor is the intracellular bile acid “sensor” and its major physiological role is to protect liver cells from the deleterious effect of Bile Acids (BA) overload. Intestine is the tissue expressing the first FXR target gene identified. Indeed IBAB-P is expressed in enterocytes and binds bile acids, thus limiting the free concentration of BA intracellularly and consequently their toxicity (Makishima M et al., Science, 1999, 284, 1362-1365). FXR is highly expressed in the liver and regulates key genes involved in BA synthesis, metabolism and transport including CYP7A1, UGT2B4, BSEP, MDR3, MRP2, ASBT, NTCP, OSTα and OSTβ in humans. One effect of FXR activation is downregulation of CYP7A1 and thus bile acid synthesis; this is accomplished through induction of SHP (short heterodimer partner) which then represses CYP7A1 transcription (Claudel T. et al., Arterioscler. Thromb. Vasc. Biol., 2005, 25, 2020-2031).
Altered expression or malfunction of these genes has been described in patients with cholestatic liver diseases. A protective role of FXR modulators during cholestasis has been postulated by several studies in various cholestatic animal models (Liu Y. et al., J. Clin. Invest, 2003, 112, 1678-1687). 6-ECDCA was found to fully reverse the impairment of bile flow and to protect the hepatocytes against liver cell injury caused by the cytotoxic lithocholic acid (Pelliciari R. et al., J. Med. Chem., 2003, 45, 3569-3572).
The process of enterohepatic circulation of bile acids is also a major regulator of serum cholesterol homeostasis. After biosynthesis from cholesterol in the liver, BA are secreted with bile into the lumen of the small intestine to aid in the digestion and absorption of fat and fat-soluble vitamins. The ratio of different BA determines the hydrophilicity of the bile acid pool and its ability to solubilize cholesterol. FXR activation increases the hydrophilicity of the pool, decreasing the intestinal solubilization of cholesterol, effectively blocking its absorption. Decrease absorption would be expected to result in lowering of plasma cholesterol levels. Indeed direct inhibitors of cholesterol absorption such as ezetimibe decrease plasma cholesterol, providing some evidence to support this hypothesis. However ezetimibe has limited efficacy which appears due to feedback up-regulation of cholesterol synthesis in cells attempting to compensate for depletion of cholesterol. Recent data have shown that FXR opposes this effect in part by directly repressing the expression of HMGCoA reductase via a pathway involving SHP and LRH1 (Datta S et al., J. Biol, Chem, 2006, 281, 807-812). In addition, Hubbert M L et al. (Hubbert M et al., Mol Endocrinol, 2007, 21, 1359-1369) reported that FXR induces the expression of hepatic Insig-2, which represses lanosterol 14alpha-demethylase, and reduces HMG-CoA reductase protein levels.
Most patients with coronary artery disease have high plasma levels of atherogenic LDL. The HMGCoA reductase inhibitors (statins) are effective at normalizing LDL-C levels but reduce the risk for cardiovascular events such as stroke and myocardial infarction by only about 30%. Additional therapies targeting further lowering of atherogenic LDL as well as other lipid risk factors such as high plasma triglyceride levels and low HDL-C levels are needed.
Thus FXR constitutes a potential therapeutic target that can be modulated to enhance the removal of cholesterol from the body.
Subsequent studies demonstrated that FXR also regulates a set of genes that control specific aspects of lipoprotein metabolism. Sinai et al. originally proposed that FXR controls plasma lipid levels (Sinai C J et al., Cell, 2000, 102, 731-44). More recently, the FXR agonist GW4064, when used to treat db/db diabetic mice, significantly reduced plasma TG (Zhang Y. et al., Proc. Natl. Acad. Sci., 2006, 103, 1006-1011). FXR activation affects TG metabolism via several pathways. Some mechanisms involved in the reduction of TG include down-regulation of the transcription factor sterol regulatory element-binding protein 1c α (Pineda-Torra I. et al., Mol. Endocrinol., 2005, 17, 259-272), down-regulation of apoC-III (Claudel T. et al., Gastroenterology, 2003, 125, 544-555), up-regulation of apoC-II (Kast H. R. et al., Mol. Endocrinol., 2001, 15, 1720-1728) and up-regulation of syndecan-1 and the VLDL receptor. Increasing fatty acid oxidation represents another means for FXR mediated reduction of plasma triglyceride levels by up-regulating pyruvate dehydrogenase kinase (PDK4) (Savkur R. S. et al., Biochem Biophys. Res. Commun., 2005, 329, 391-6).
Furthermore, the studies of Edwards P. A. et al. (J. Lipid Res, 2002, 1, 2-12) showed that FXR alters the transcription of several genes involved in fatty acid and triglyceride synthesis, as well as lipoprotein metabolism. These genes include the phospholipid transfer protein (PLTP), the syndecan-1 (SDC-1) and the very low density lipoprotein receptor (VLDLR) (Urizar N. L. et al., J. Biol. Chem., 2000, 275, 39313-39317; Anisfeld A. M. et al., J. Biol. Chem., 2003, 278, 20420-20428; Sirvent A. et al., FEBS Lett., 2004, 566, 173-177). Recently new FXR modulator compounds show the ability to reduce both plasma triglyceride and cholesterol levels in normal and hyperlipidemic animal models (see e.g., International Patent Application Publication No. WO 2007/070796).
Thus compounds which modulate FXR activity may show superior therapeutic efficacy on plasma cholesterol and triglyceride lowering than current therapies.
FXR activation has also been described to downregulate proinflammatory enzymes iNOS and COX-2, as well as migration of vascular smooth muscle cell migration (Li YTY et al., Arterioscler Thromb Vasc Biol., 2007, 27, 2606-2611). This protective effect of FXR agonists on atherosclerosis plaque stability may be of valuable interest also in the treatment of inflammation in diabetic nephropathy.
Interesting results have been obtained with BA sequestrants in a randomized, double band crossover trial. The administration of cholestyramine improved glycemic control in patients with type 2 diabetes and dyslipidemia (Garg A et al., Ann Intern Med, 1994, 121, 416-422). Several recent studies have demonstrated that FXR plays a role in glucose metabolism. Mice treated with GW4064 or cholic acid or after infection with a FXR-VP16 fusion protein adenovirus resulted in a significant decrease of plasma glucose levels and improved insulin sensitivity in three diabetic models (db/db, ob/ob and KK-A(y) mice) (Cariou B. et al., J. Biol. Chem., 2006, 281, 11039-11049; Zhang Y. et al., Proc. Natl. Acad. Sci., 2006, 103, 1006-1011; Ma K. et al., J. Clin. Invest., 2006, 116, 1102-1109). Consistent with these data, Fxr mice show impaired glucose tolerance and insulin resistance (Cariou B. et al., J. Biol. Chem., 2006, 16, 11039-11049). FXR expression is also stimulated by glucose and repressed by insulin in rat primary hepatocytes (Duran-Sandoval D. et al., Diabetes, 2004, 53, 890-898). GW4064 treatment reduces phosphoenol pyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6 Pase) expression in diabetic db/db mice but GW4064 induces PEPCK expression and increases glucose output in primary hepatocytes in vitro (Stayrook K. R. et al., Endocrinology, 2005, 146, 984-991).
In the case of diabetes of the type 2 elevated blood glucose per se is associated with increased and premature mortality due to an increased risk for microvascular and macrovascular diseases, including retinopathy (the impairment or loss of vision due to blood vessel damage in the eyes); neuropathy (nerve damage and foot problems due to blood vessel damage to the nervous system); and nephropathy (kidney disease due to blood vessel damage in the kidneys), hypertension, cerebrovascular disease and coronary heart disease. Therefore, control of glucose homeostasis is an important approach for the treatment of diabetes. Thus, FXR modulators have been disclosed as useful for the treatment, prevention, or amelioration of one or more of the symptoms of insulin insensitivity or resistance or for the treatment of the complications of hyperglycemia (see, e.g., International Patent Application Publication No. WO 01/82917) Based on these findings, FXR selective modulators are potential pharmaceutical candidates for the management of type 2 diabetes and hypertriglyceridemia, which are two major symptoms of metabolic syndrome.
FXR modulators are also suitable for treating obesity, as well as for treating the complications of obesity. The terms “obese” and “obesity” refer to, according to the World Health Organization, a Body Mass Index (BMI) greater than 27.8 kg/m2 for men and 27.3 kg/m2 for women (BMI equals weight (kg)/height (meters squared). Obesity is linked to a variety of medical conditions including diabetes and an atherosclerotic disease event. (See, e.g., Barrett-Conner E., Epidemiol. Rev., 1989, 11, 172-181; Tulloch-Reid M. K. et al., Diabetes Care, 2003, 26, 2556-2561).
Recent studies have demonstrated the involvement of FXR in cancer pathology as liver cancer (Yang F. et al., Cancer Res., 2007, 67, 863-867); breast cancer (Swales K. E. et al., Cancer Res., 2006, 66, 10120-10126); colorectal cancer (De Gottardi A. et al, Dig Dis Sci 2004, 49, 982-989; Debruyne P. R. et al., Oncogene 2002, 21, 6740-6750); esophagus cancer (De Gottardi A. et al., Mol Cancer, 2006, 5, 48-57).
Nuclear receptor activity, including the farnesoid X receptor and/or orphan nuclear receptor activity, has been implicated in a variety of diseases and disorders, including, but not limited to disorders of the skin and mucous membranes and acne (see, e.g., U.S. Pat. Nos. 6,071,955 and 6,187,814), Parkinson's disease (Sacchetti P. et al., Nucleic Acids Res., 2006, 34, 5515-5527) and Alzheimer's disease (Wolozin B., Neuron, 2004, 41, 7-10).
Thus, there is a need for novel classes of compounds that possess the beneficial properties. It has been discovered that a class of compounds, referred to herein as compounds of formula (I), are useful as agents for treating or preventing various diseases or disorders disclosed herein.